The invention relates to a control valve for controlling an overflow of a medium from a first pressure space into a second pressure space having a pressure different from a pressure in the first pressure space, with a valve body prestressed against a valve seat, with a control device for moving the valve body and with a movable pressure compensating element which is subjected to the pressure difference between the pressure spaces and is connected to the valve body and which is intended for compensating the pressure forces acting on the valve body.
Such electromagnetic control valves are used, for example, in devices for exhaust-gas recirculation in internal combustion engines of present-day motor vehicles. In this case, the pressure spaces take the forms of the intake duct and the exhaust duct of the internal combustion engine. In such devices for exhaust-gas recirculation, a part stream of exhaust gas is branched off from the exhaust duct and is supplied to the intake duct. The nitrogen fraction in the exhaust gas can thereby be reduced. The ratio of the exhaust-gas quantity to be supplied to the fresh-air quantity depends on, for example, the load state, the temperatures or the rotational speed of the internal combustion engine and is determined by the control of the valve body. For this control, the control device has, for example, a pneumatic, electromagnetic or electromotive actuating drive.
In order to avoid particularly high actuating forces during the movement of the valve body when there are high pressure differences between the pressure spaces, a control valve has become known from practice, in which a second valve body is designed as a pressure compensating element. The valve bodies are fastened on a common valve shaft and, in the basic position, in each case bear on a valve seat. One of the pressure spaces is connected to the region between the valve bodies, whilst the regions on those sides of the valve bodies which face away from one another are connected to the other pressure space. As a result, forces generated due to pressure differences in the pressure spaces act in each case on the valve shaft, but in opposite directions of force.
A disadvantage of the known control valve is that the respective distances between the valve bodies and the valve seats must have particularly low tolerances. Moreover, for example, in the event of thermal expansion of the valve shaft or wear of the valve bodies and of the valve seats, the control valve does not reliably seal off the pressure spaces from one another. Different expansions of the valve bodies and the valve seats likewise result in leaks.
The problem on which the invention is based is to provide a control valve of the type initially mentioned, in such a way that it does not need low tolerances and reliably seals off the pressure spaces relative to one another.
This is solved, according to the invention, in that the pressure spaces are sealed off relative to one another in the region of the pressure compensating element.
By virtue of this provide, the control valve according to the invention has a single valve body. The valve body and the pressure compensating element are separated from one another as result of the invention. The control valve according to the invention therefore does not need to have particularly low tolerances. A leak in the control valve according to the invention can consequently be avoided in a simple way. The control valve according to the invention is therefore suitable, in particular, for use in a device for exhaust-gas recirculation in an internal combustion engine of a motor vehicle.
The pressure compensating element could, for example, be a piston displaceable in a cylinder arranged between the pressure spaces. According to another advantageous development of the invention, the pressure compensating element reliably seals off the two pressure spaces relative to one another if the pressure compensating element has a diaphragm for separating the pressure spaces.
According to another advantageous development of the invention, the pressure compensating element has a particularly simple construction if a valve shaft designed for adjusting the valve body is connected to a disk holding the diaphragm.
According to another advantageous development of the invention, disturbances of the pressure compensating element which are generated by flows within the pressure spaces can reliably be avoided if the pressure compensating element subdivides a container into two chambers, and if the first chamber is connected to the first pressure space and the second chamber to the second pressure space.
The control valve according to the invention has a particularly compact formation if the container is arranged on that side of the first pressure space which is located opposite the second pressure space, and if a pressure compensating duct connects the second pressure space to the second chamber.
When the control valve according to the invention is in the basic position, particularly reliable sealing off of the pressure spaces can be ensured in a simple way if the valve body is capable of being returned into the closing position by means of a spring element. The spring element may be manufactured, for example, from spring steel. Since the spring element has to transmit only very low return forces, it may also consist of a metal memory alloy.
According to another advantageous development of the invention, an equilibrium of the forces acting on the valve body and on the pressure compensating element can be established in a simple way if a lever is arranged between the valve body and the pressure compensating element.